The present invention is directed to a road-finishing machine for laying a road-finishing material on a prepared surface in an even, uniform, and level manner and, in particular, to such a road-finishing machine having, for example, one directional wheel on each side and being provided with level compensation which does not rely on having the directional wheels coupled to a rocker extending transversely to the direction of travel.
Road-finishing machines fitted with a wheeled under-carriage have a set of driving wheels for providing motive power as well as a set of directional wheels for enabling a change in direction. Some versions of such a road-finishing machine have two directional wheels on each side, while other versions typically have only one directional wheel on each side. The road-finishing material is retained in a bucket from which the material is transported to a laying beam by a scraper belt. In order to facilitate formation of a smooth roadway, the road-finishing material must be applied in an even and level manner. Consequently, the road-finishing machine includes some type of level compensation arrangement which maintains the frame of the road-finishing machine level even though the wheels move vertically as they encounter bumps or holes. In the arrangement having two directional wheels on each side, good automatic leveling characteristics, as well as uniform load distribution on the directional wheels, are attained by engaging the two directional wheels on each side in a common rocker which operates longitudinally to the direction of travel. If, however, the road-finishing machine has only one directional wheel on each side, these are usually connected rigidly to the road-finishing machine frame, i.e. without level compensation. However, level compensation for a road-finishing machine having only one directional wheel on each side is available in the prior art by mounting the two directional wheels (i.e. on opposite sides of the frame) in a common rocker which is arranged transversely to the direction of travel.
In order to minimize loading difficulties for the road-finishing machine, the bucket floor must be positioned as close as possible to the roadway. On the other hand, sufficient ground clearance for the road-finishing machine must also be provided. Consequently, little room is available for anything which must be placed below the bucket. The scraper belt is positioned in this area. When a transverse rocker is used, it must fit between the upper and lower portions of the scraper belt as the rocker extends transversely from one side of the road-finishing machine to the other.
The transverse rocker must have large lever arms having very high resistance moments. It must withstand forces applied when the bucket is loaded by rear dumper trucks which, as they unload, support themselves partially on the bucket floor, depending on the projection of the loading surface, so that the rear wheels of the truck can, in fact, be up in the air. Strength of the rocker is related to its size. It must be made bigger in order for it to be stronger. However, the requirement for a very strong transverse rocker conflicts with the very limited amount of space available to accommodate it. For this reason, a transverse rocker is dispensed with if possible. If the transverse rocker is eliminated, however, no level compensation is provided for the road-finishing machine.
Level compensation is very important, particularly when only two directional wheels in total are provided, because of the small contact surface with the roadway resulting from having one wheel being out of contact therewith. Furthermore, if one of the two directional wheels is heavily loaded in comparison to the other, it will sink into the relatively loose roadway subsoil. This creates not only uneveness in the surface being laid because of the roadway subsoil being pushed up in the area of the periphery of the sunken directional wheel, but also results in the possibility of the other directional wheel having no ground contact whatsoever because it is lifted up in the air.